The bottom cabinet in these built-ins was never finished (Photo 1).

Photo 2 is a vertical look up the chase behind the cabinet. To the rear is a poorly insulated exterior wall. At the top of the chase, to the left is an unvented flat roof above a first floor addition. At the top of the chase, to the right is the second story of the house.

This entire area feels very leaky.

How would you air seal this space?

I have already foamed around the pipe penetrations at the bottom of the cabinet and was considering using rigid foam board to create a horizontal block in the chase, or perhaps trying to access from above (which would be equally tricky). I’ll also spray foam at least seams along the exterior wall.

Thank you.